Sleep Apnea (cont.)

Siamak N. Nabili, MD, MPH

Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What are the types of sleep apnea?

During sleep, the brain instructs the muscles of breathing to take a breath.

Central sleep apnea (CSA) occurs when the brain does not send the signal to the muscles to take a breath and there is no muscular effort to take a breath.

Obstructive sleep apnea (OSA) occurs when the brain sends the signal to the muscles and the muscles make an effort to take a breath, but they are unsuccessful because the airway becomes obstructed and prevents an adequate flow of air.

Mixed sleep apnea, occurs when there is both central sleep apnea and obstructive sleep apnea.

What is central sleep apnea and what causes it?

Central sleep apnea (CSA) occurs when the brain does not send the signal to breathe to the muscles of breathing. This usually occurs in infants or in adults with heart disease, cerebrovascular disease, or congenital diseases, but it also can be caused by some medications and high altitudes.

Central sleep apnea may occur in premature infants (born before 37 weeks of gestation) or in full-term infants. It is defined as apneas lasting more than 20 seconds, usually with a change in the heart rate, a reduction in blood oxygen, or hypotonia (general relaxation of the body's muscles). These children often will require an apnea monitor that sounds an alarm when apneas occur. Central sleep apnea in children is not the same thing as sudden infant death syndrome (SIDS).

Under normal circumstances, the brain monitors several things to determine how often to breathe. If it senses a lack of oxygen or an excess of carbon dioxide in the blood it will speed up breathing. The increase in breathing increases the oxygen and decreases the carbon dioxide in blood. Some people with heart or lung disease have an increase in carbon dioxide in their blood at all times.

When there is a chronic (long-term) increase in blood carbon dioxide, the brain starts to ignore the oxygen level and monitors the blood carbon dioxide level to determine when to take the next breath. The control of breathing also becomes slower to respond to changes in carbon dioxide levels; so when a person takes more or deeper breaths and "blows off" carbon dioxide the drive to breathe decreases and the rate of breathing decreases. As a result of slower rate of breathing, carbon dioxide builds back up in the blood and the rate of breathing increases again. The brain, slow to adjust, continues to signal for more rapid breathing until the carbon dioxide level drops too low. Breathing then slows down or stops until the carbon dioxide level rises again. This pattern of abnormal breathing is called Cheyne-Stokes breathing (after the men who described it). It is characterized by repetitive cycles of fast breathing followed by slow breathing and apnea. This breathing pattern happens when the person is awake or asleep, but becomes more of a problem when asleep. Some patients with heart failure have central sleep apnea associated with a Cheyne-Stokes pattern of breathing.

Central sleep apnea usually occurs in adults with other medical problems. In infants, it usually occurs with prematurity or other congenital disorders. In both patient groups it is usually suspected by the primary care doctor. Central sleep apnea can be diagnosed with a sleep study or overnight monitoring while the patient is in the hospital.

In infants, central sleep apnea is treated with an apnea alarm. This alarm monitors the infant's breathing with sensors and sounds a loud noise when the infant experiences an apnea. The alarm usually wakes the infant and the parents. Most infants usually "out-grow" the central apnea episodes, so the alarm monitoring is stopped after the episodes resolve. In infants with other congenital problems, apnea monitoring may be needed for a longer period.

In adults with central sleep apnea, the apneas are treated by treating the underlying heart disease, medication interaction, high altitude, or other primary problem.